1. Limited Copyright Waiver
A portion of the disclosure of this patent document contains material to which the claim of copyright protection is made. The copyright owner has no objection to the facsimile reproduction by any person of the patent document or the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent file or records, but reserves all other rights whatsoever.
2. Field of the Invention
The present invention relates to systems providing an interface and establishing access paths between users of data in a data processing system and facilities storing such data. In particular, the present invention provides a file system adaptable to optimize use of a plurality of access paths and available storage hardware to meet operational requirements of the system.
3. Description of Related Art
Computer systems are being developed in which the amount of data to be manipulated by the system is immense. For instance, data storage systems have been proposed that are capable of handling amounts of data on the order of exabytes, spread across hundreds of direct access storage devices (DASDs). Individual files for such systems have been proposed to be as high as ten gigabytes (10.sup.10 bytes) Such large storage systems should be very reliable, since restoring an entire storage system after a crash could take many hours or days. In addition, these storage systems should sustain very high data transfer rates to allow for efficient use of the data. Further, it is desirable that there be no single point of failure which could cause such a large data system to go out of service. The requirements for size, speed and reliability of such data systems will continue to keep pace with increases in capacity of supercomputers at the high end, and with increasing numbers of large data storage systems being used by slower computers.
Prior art file systems which provide an interface between users of data, buffers in the computer system and external storage to the computer system, have operated by establishing a single access path for any individual request by a user to a file. This is absolutely reasonable as long as there are very few devices storing the data. But, in configurations with many storage devices and many independent access paths through which the data may be transferred in parallel in response to each individual request, the one access path per request limitation of system control programs greatly restricts the response time for a given task requiring transfer of data between external to internal storage.
Prior art file systems can be characterized with reference to the diagram shown in FIG. 1. The computer system in which the prior art file system runs would include a plurality of application programs A, corresponding to users of data. Some of the application programs will be part of processing subsystems (SS), such as database drivers and the like. These application programs A, or subsystems, will generate access requests through a user interface I, to the buffer space in the computer. If data required by a given transaction is not located in the buffer space, then the system control program SCP establishes an access path through device drivers by which the required data can be retrieved from non-volatile storage.
Management of the buffer space is a major operational bottleneck for data processing systems with multiple users and large numbers of data files. In UNIX, the buffer space is managed in a least recently used manner, such that when the buffer space is full, a page is released from the buffer according to a simple algorithm to make space for the current transaction. However, there is no guarantee that the space being released is not critical data for another program running in the system, because all users share the same buffer pool. Also, when very large migration of data takes place, the buffer pool can be quickly depleted for use by the migration transaction, effectively locking out other users of the system during the migration.
In other operating systems, such as MVS, the buffer space is allocated to a group of buffer pools. Each buffer pool is managed essentially independently by the users or subsystems accessing the buffer space. By dividing up the buffer space among users, better control over availability of pages of data can be exercised, such as required in transaction control systems that perform a journal function for each transaction. However, by statically allocating buffer space among a plurality of users, inefficiencies arise that influence the overall performance of the data processing system. For instance, a given subsystem may be active during a particular time of day and inactive during another time. However, without action on the part of the subsystem, its buffer space will remain allocated throughout the day leaving a large amount of buffer space unavailable for use.
The problem of efficiently allocating buffer space among users in MVS-based systems is a major operational problem that consumes a great deal of resources and renders operation of the data processing system extremely complex to users.
Accordingly, a file system is needed that is capable of exploiting large numbers of access paths, and providing efficient access to files which range in size from a few bytes to hundreds of gigabytes and beyond. The file system must be extended to allow for efficient journaling of transactions and database processing. Also, it is desirable that operation of the file system be convenient and automated and that it be adaptable to emerging storage device technology. Further, it is desirable to provide a file system that will allow continuous access to data concurrently with maintenance, migration and error correction on files being used.